Magnesium alloy member and method for making the same

ABSTRACT

An exemplary magnesium alloy member superior in corrosion resistance includes a magnesium alloy base, at least one resin coating layer formed in at least one portion of the magnesium alloy base. Methods for making the magnesium alloy member are also provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates, generally, to a magnesium alloy member, and particularly to a magnesium alloy member superior in corrosion resistance.

2. Discussion of the Related Art

Magnesium alloys have been attracting attention as having a number of excellent practical properties for use as structural materials. Magnesium is practically lighter, stronger, and stiffer than iron and aluminum. Magnesium alloys have highest capability in absorbing vibrations (damping capacity) among popular metal materials (Fe, Al and so on), highly resistant to dint, less likely to deform with time or temperature, and easily recyclable. For these reasons, magnesium alloy is suitable as structural material for vehicles and for housing of portable terminals.

Because magnesium alloy is the most common popular alloy, when screwed or fastened together with different metals such as iron and aluminum, electrolytic corrosion is likely due to moisture in electrolytes in rain, melted snow, salt, etc. In particular, inside the hood and on the inside surface of the body of automobiles, electrolytic corrosion happens more frequently due to the electrolytes. Electrolytic corrosion may cause fastened parts to be come loosened/detached.

Referring to FIG. 5, a typical AZ91D magnesium alloy sheet 12 and a metallic sheet 14 are fastened with a steel bolt 16 and a nut 17 between three aluminum washers 18. In order to decrease electrolytic corrosion between the magnesium alloy sheet 12, the bolt 16 and the washers 18, the washers 18 may be insulated by anodic oxidation, or, the steel bolt 16 may be coated with resin. However, performing anodic oxidation on the washers 18 is very expensive, and the bonding strength and durability on resin coated steel bolts 16 is weak.

What is needed, therefore, is a new magnesium alloy member that can decreasing electrolytic corrosion when contact with different metals. A method for making the new magnesium alloy is also desired.

SUMMARY

In one aspect, a magnesium alloy member superior in corrosion resistance according to a preferred embodiment includes a magnesium alloy base, at least one resin coating layer formed in at least one portion of the magnesium alloy base.

In another aspect, a method for making the magnesium alloy member described in a previous paragraph includes: providing a magnesium alloy base; forming at least one resin coating layer on at least a part of surfaces of the magnesium base.

Other advantages and novel features will become more apparent from the following detailed description of the preferred embodiments, when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present magnesium alloy member superior in corrosion resistance and method for making the magnesium alloy. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views, and all the views are schematic.

FIG. 1 is a partial cross-sectional view of a magnesium alloy member according to a first preferred embodiment of the present invention, the magnesium alloy member coupled with a metallic sheet by a bolt and a nut of a dissimilar material.

FIG. 2 is a partial cross-sectional view of a mold for making the magnesium alloy member of FIG. 1 with a magnesium alloy preform in the mold.

FIG. 3 is a partial cross-sectional view of a magnesium alloy member according to a second preferred embodiment of the present invention, the magnesium alloy member coupled with two metallic members by a bolt and a nut of a dissimilar material.

FIG. 4 is a cross-sectional view of a mold for making the magnesium alloy member of FIG. 3 with a magnesium alloy preform in the mold.

FIG. 5 is an partial, side view of a conventional magnesium alloy sheet coupled with a metallic sheet by a bolt and a nut of a dissimilar material.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to the drawings to describe preferred embodiments of the present magnesium alloy member superior in corrosion resistance and methods for making the magnesium alloy member, in detail.

Referring to FIG. 1, a magnesium alloy member 20 in accordance with a first preferred embodiment of the present invention is shown. The magnesium alloy member 20 and a metallic sheet 29 are fastened together using a steel bolt 27 and a nut 28. The magnesium alloy member 20 includes a magnesium alloy base 21, a polyethylene foam layer 23 and a polyethylene rigid layer 25. In this embodiment, the magnesium alloy base 21 further includes a plurality of micro-protrusions 212 protruding from opposite surfaces of a fastening end of the magnesium alloy base 21. The polyethylene foam layer 23 and the polyethylene rigid layer 25 are coated around the fastening end in that order. A thickness of the polyethylene foam layer 23 is thicker than a height of the micro-protrusions 212. In other words, the micro-protrusions 212 are embedded in the polyethylene foam layer 23, and this increases the bonding strength between the magnesium alloy base 21 and the polyethylene foam layer 23. The polyethylene rigid layer 25 completely covers and protects the polyethylene foam layer 23.

The fastening end of the magnesium alloy member 20 and the metallic sheet 29 defines a through hole 214 correspondingly. The magnesium alloy member 20 and the metallic sheet 29 are fastened tightly by inserting the bolt 27 through the through hole 214 and tightening the nut 28 on the end of the bolt 27. In this embodiment, an inner width of the through hole 214 of the magnesium alloy member 20 is greater than a width of the steel bolt 27, such that the steel bolt 27 can be inserted and bolted without coming in contact with an inside surface of the magnesium alloy base 21.

In alternative embodiments, the magnesium alloy base 21 may define a plurality microstructures, including grooves, through holes, or embossed microstructures instead of the micro-protrusions 212. The microstructures also increase the bonding strength between the magnesium alloy base 21 and the polyethylene foam layer 23.

A method for making the magnesium alloy member 20 includes following steps:

Firstly, a magnesium alloy base 21 is manufactured by casting, forging, or extrusion molding methods to form any shape. In this embodiment, the magnesium alloy base 21 is L-shaped. The magnesium alloy base 21 has micro-protrusions 212 formed at opposite surfaces of the fastening end thereof.

Secondly, the polyethylene foam layer 23 is coated around the end portion of the magnesium alloy base 21. Referring to FIG. 2, a mold 30 and an injection machine (not shown) is provided. The mold 30 has a first cavity 32. The end portion of the magnesium alloy base 21 having the micro-protrusions 212 is positioned in the first cavity 32 for defining a suitable space to form the polyethylene foam layer 23. A feed substantially consisting of about 90% wt. of polyethylene pellets to about 10% wt. of foaming agent (such as sodium bicarbonate) is uniformly mixed. This feed is fed to a heating cylinder (not shown) of the injection machine and heated to a melted state of about 90° C. degrees. When the feed is heated, carbon dioxide gas is produced from the sodium bicarbonate and enters the melted feed, thereby forming a plurality of air pockets in the melted feed. The melted feed is pushed by the elongated screw of the injection machine at a relative high pressure to shot out via a nozzle of the injection machine into the first cavity 32 of the mold 30. After cooling the mold 30, a polyethylene foam layer 23 coats around the fastening end of the magnesium alloy base 21 (a magnesium alloy preform) is achieved.

Thirdly, the polyethylene rigid layer 25 is coated around the polyethylene foam layer 23 of the magnesium alloy preform. This step is similar to the previous step of forming the polyethylene foam layer 23. A second mold (not shown) having a second cavity (not shown) is provided. The end portion forming the polyethylene foam layer 23 of the second magnesium alloy preform is positioned in the second cavity having a shape of the polyethylene rigid layer 25. Polyethylene pellets are fed to the heating cylinder of the injection machine for heating the polyethylene to a melted state of about 95° C. degrees. The melted polyethylene is pushed by the elongated screw at a relative high pressure to shot out via a nozzle of the injection machine into the second cavity of the second mold. Finally, after cooling the mold, a polyethylene rigid layer 25 on the polyethylene foam layer 23 is produced.

In use, the bolt 27 is insulated from the magnesium alloy base 21 with the polyethylene foam layer 23 and the polyethylene rigid layer 25, accordingly, electrolytic corrosion between the magnesium alloy member 20 and the bolt 27 is reduced, or even eliminated (prevented). The polyethylene foam layer 23 is configured for insulating the magnesium alloy base 21 and further having good heat resistance property. The polyethylene rigid layer 25 has a good mechanical strength for protecting the polyethylene foam layer 23. The magnesium alloy member 20 is suitable for a structural element for vehicles.

Referring to FIG. 3, a magnesium alloy member 40 in accordance with a second preferred embodiment of the present invention is shown. The magnesium alloy member 40 is used as an oil pan for protecting an engine of automobile. The magnesium alloy member 40 includes a magnesium alloy base 41, a methylene di-phenyl diisocyanate foam layer (hereinafter named MDI foam layer) 43 and a polyurethane rigid layer (hereafter named PU rigid layer) 45. The magnesium alloy base 41 has a hat-shaped with a hat flange cross-section. The MDI foam layer 43 and the PU rigid layer 45 are respectively coated surfaces of the magnesium alloy base 41 in that order. A thickness of the MDI foam layer 43 is greater than that of the PU rigid layer 45. The MDI foam layer 43 is configured for increasing heat resistance character. PU rigid layer 45 is configured for protecting the MDI foam layer 43 and providing rigid character.

Two ends of the magnesium alloy member 40 are respectively fastened to two metallic members 49 of dissimilar material with two bolts 47 and two nuts 48.

A method for making the magnesium alloy member 40 includes following steps.

Firstly, a magnesium alloy base 41 is manufactured by casting, forging, or extrusion molding methods to form different predetermined shapes.

Secondly, the MDI foam layer 43 is coated on surfaces of the magnesium alloy base 41. Referring to FIG. 4, a mold 60 and an injection machine (not shown) is provided. The mold 60 includes a first cavity 62. The magnesium alloy base 41 is positioned in a center of the first cavity 62 by a plurality of spacers 64, thereby, defining a foam space to form the MDI foam layer 43. A feed, substantially consisting of 85% wt. MDI pellets and 15% wt. of foaming agent (such as trichlorofluoromethane) uniformly mixed, is fed to a heating cylinder (not shown) of the injection machine for heating the feed to a melted state of about 160° C. degrees. When the feed is heated, gas is produced from the trichlorofluoromethane and enters the melted feed, thereby forming a plurality of air pockets in the melted feed. The melted feed is pushed by an elongated screw of the injection machine at a relative high pressure to shot out via a nozzle of the injection machine into the first cavity 62 of the mold 60. After cooling the mold 60, a MDI foam layer 43 coated on the surfaces of the magnesium alloy base 41 (a magnesium alloy preform) is achieved.

Thirdly, the PU rigid layer 45 is coated on the MDI foam layer 43. This step is similar as the previous step of forming the MDI foam layer 43. A second mold (not shown) having a second cavity (not shown) is provided. The magnesium alloy preform is positioned in the second cavity for defining a suitable space to form the PU rigid layer 45. Polyurethane pellets are fed to the heating cylinder of the injection machine for heating the polyurethane to a melted state. The melted polyurethane is fed to the heating cylinder (not shown) of the injection machine and is pushed by the elongated screw at a relative high pressure, and is shot out via a nozzle of the injection machine into the second cavity of the second mold. Finally, after cooling the mold, a PU rigid layer 45 on the MDI foam layer 43 is achieved.

It should be pointed out that at least two resin coating layers (such as polyethylene foam layer 23, polyethylene rigid layer 25, MDI foam layer 43, and PU rigid layer 45) can be laminated on at least a part of the magnesium alloy base by one of adhesive bond, fusion bond, and so on. Material of the resin coating layers is selected from a group consisting of polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polyurethane (PU), urea formaldehyde (UF), phenol formaldehyde resin (PF), ethylene resin (ER), acrylonitrile-butadiene-styrene (ABS), polymethyl methacrylate (PMMA), polycarbonate (PC), polytetrafluoroethylene (PTFE), polyimide (PI), and their combination. In addition, many additive agents can be mixed into at least one of the resin coating layers for increasing any other characters, such as density, light, rigid, heat resistance, or sound insulation characters.

Finally, while the present invention has been described with reference to particular embodiments, the description is illustrative of the invention and is not to be construed as limiting the invention. Therefore, various modifications can be made to the embodiments by those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims. 

1. A magnesium alloy member superior in corrosion resistance comprising: a magnesium alloy base, and at least one resin coating layer formed in at least one portion of the magnesium alloy base.
 2. The magnesium alloy member superior in corrosion resistance according to claim 1, wherein the at least one resin coating layer comprises a polyethylene foam layer and a polyethylene rigid layer, the polyethylene foam layer and the polyethylene rigid layer coated around at least one portion of the magnesium alloy base.
 3. The magnesium alloy member superior in corrosion resistance according to claim 2, wherein the magnesium alloy base defines a plurality of microstructures on at least one portion of surfaces thereof, the microstructures consisting of grooves, through holes, micro-protrusions, or embossed microstructures.
 4. The magnesium alloy member superior in corrosion resistance according to claim 3, wherein the micro-protrusions protrude from two opposite surfaces of the magnesium alloy base, the micro-protrusions inserted into the polyethylene foam layer.
 5. The magnesium alloy member superior in corrosion resistance according to claim 1, wherein the at least one resin coating layer comprises a methylene di-phenyl diisocyanate foam layer and a polyurethane rigid layer, the methylene di-phenyl diisocyanate foam layer and the polyurethane rigid layer coated around at least one portion of the magnesium alloy base.
 6. The magnesium alloy member superior in corrosion resistance according to claim 1, wherein a material of the at least one resin coating layer is selected from a group consisting of polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyurethane, urea formaldehyde, phenol formaldehyde resin, ethylene resin, acrylonitrile-butadiene-styrene, polymethyl methacrylate, polycarbonate, polytetrafluoroethylene, polyimide, and their combination.
 7. The magnesium alloy member superior in corrosion resistance according to claim 1, wherein the at least one resin coating film has at least one additive agent for increasing a group character consisting of density, light, rigid, heat resistance, or sound insulation characters.
 8. A method for making a magnesium alloy member superior in corrosion resistance, comprising: providing a magnesium alloy base; forming at least one resin coating layer on at least a part of the magnesium base.
 9. The method for making a magnesium alloy member superior in corrosion resistance as claimed in claim 8, wherein the at least one resin coating layer including a polyethylene foam layer and a polyethylene rigid layer, the polyethylene foam layer and the polyethylene rigid layer coated around at least one portion of the magnesium alloy base, the step for forming the polyethylene foam layer and the polyethylene rigid layer coated around at least one portion of the magnesium alloy base comprises sub-steps: providing an injection machine and a first mold defining a first cavity; placing the magnesium alloy base into the first cavity for defining a suitable space for forming the polyethylene foam layer; mixing and heating a first feed including polyethylene pellets and foaming agent to a first melted feed; injecting the first melted feed into the first cavity for forming the polyethylene foam layer on the magnesium alloy base by the injection machine, thereby a magnesium alloy preform is achieved; providing a second mold defining a second cavity; placing the magnesium alloy preform into the second cavity for defining a suitable space for forming the polyethylene rigid layer; heating polyethylene pellets to a second melted feed; and injecting the second melted feed into the second cavity for forming the polyethylene rigid layer on the polyethylene foam layer by the injection machine, thereby the magnesium alloy member is achieved.
 10. The method for making a magnesium alloy member superior in corrosion resistance as claimed in claim 9, wherein the foaming agent is sodium bicarbonate.
 11. The method for making a magnesium alloy member superior in corrosion resistance as claimed in claim 9, wherein the first feed consists of about 90% wt. polyethylene pellets and about 10% wt. foaming agent.
 12. The method for making a magnesium alloy member superior in corrosion resistance as claimed in claim 9, wherein the first feed is heated to a melted state of about 90 degrees C.
 13. The method for making a magnesium alloy member superior in corrosion resistance as claimed in claim 8, wherein the at least one resin coating layer including a methylene di-phenyl diisocyanate foam layer and a polyurethane rigid layer, the step for forming the methylene di-phenyl diisocyanate foam layer and the polyurethane rigid layer coated around at least one portion of the magnesium alloy base comprises sub-steps: providing an injection machine and a first mold defining a first cavity; placing the magnesium alloy base into the first cavity for defining a suitable space for forming the polyethylene foam layer; mixing and heating a first feed including methylene di-phenyl diisocyanate pellets and foaming agent to a first melted feed; injecting the first melted feed into the first cavity for forming the methylene di-phenyl diisocyanate foam layer on the magnesium alloy base by the injection machine, thereby a magnesium alloy preform is achieved; providing a second mold defining a second cavity; placing the magnesium alloy preform into the second cavity for defining a suitable space for forming the polyurethane rigid layer; heating polyurethane pellets to a second melted feed; and injecting the second melted feed into the second cavity for forming the polyurethane rigid layer on the methylene di-phenyl diisocyanate foam layer by the injection machine, thereby the magnesium alloy member is achieved.
 14. The method for making a magnesium alloy member superior in corrosion resistance as claimed in claim 13, wherein the foaming agent is trichlorofluoromethane.
 15. The method for making a magnesium alloy member superior in corrosion resistance as claimed in claim 13, wherein the first feed consists of about 85% wt. methylene di-phenyl diisocyanate pellets and about 15% wt. foaming agent.
 16. The method for making a magnesium alloy member superior in corrosion resistance as claimed in claim 1, wherein a material of the at least one resin coating layer is selected from a group consisting of polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyurethane, urea formaldehyde, phenol formaldehyde resin, ethylene resin, acrylonitrile-butadiene-styrene, polymethyl methacrylate, polycarbonate, polytetrafluoroethylene, polyimide, and their combination
 17. The method for making a magnesium alloy member superior in corrosion resistance as claimed in claim 16, wherein at least one additive agent is mixed uniformly into the material of the at least one resin coating layer for increasing one of density, light, rigid, heat resistance, or sound insulation characters. 